Electrochemical performance of mechanochemically prepared polyaniline doped with lithium salt

Oxides and phosphates of transition metals are now predominant cathode materials of lithium-ion batteries. Organic redox active materials, conducting polymers in particular, could be a more environmentally friendly alternative. But their electrochemical characteristics were of insufficient level as to the charge capacity, rate capability and cyclability. Here, electrochemical performance of lithium salt doped polyaniline samples prepared by mechanochemical and chemical methods is comparatively analyzed as an active component of cathode masses of lithium batteries. It is shown that mechanochemically prepared polyaniline possesses specific capacity close to the theoretical limit as well as high rate capability and cyclability during prolonged charge–discharge.     

Ferroelastic phase transitions in some high-temperature superconductors with perovskite-like structure

The behaviour of low-frequency shear modulus of the La_2xSr_xCuO₄ compound with x = 0 and 0.15 in the vicinity of improper ferroelastic phase transition has been studied by the method of inverse torsion pendulum.     

A Numerical Simulation to Propose a Flash Method for In Situ Detection of the Thermal Diffusivity of Anisotropic Thin Film Materials

Strong anisotropy of thermal diffusivity is frequently observed in thin film materials. We propose an in situ experimental method to remotely measure radial and axial components of the thermal diffusivity. The method is based on the traditional laser flash technique but is specialized to also highly challenging experimental situations such as sample manufacture and use phase when thin films may be exposed to very high pressures or temperatures and to high temperature gradients. The method requires laser pulses of very short duration and fast measurement of transient temperature excursions in only radial directions on the surface of the thin film samples. The accuracy of the method is checked by comparison with results from a finite element calculation for a graphite sheet with high anisotropic conductivity that simulates a thermo-physical experiment.     

Evaluation of layer properties of effective parameters of metallic rod metamaterials in GHz frequencies

In this paper, analytical modeling and numerical simulation of the complex effective dielectric, magnetic constants and refractive index of a metallic rod metamaterial in microwave frequency range are presented. Analytical modeling has been done using modified mathematical models of the complex dielectric and magnetic constants obtained for rod metamaterial structure. Numerical simulation of the above-mentioned parameters has been made using S-parameters obtained with the help of finite-difference time-domain (FDTD) calculations. The numerical simulation has been carried out for different thickness of rods. Remarkable coincidence between analytical and numerical results was found. The effective dielectric constant enhancement of the considered composite has been obtained. Recommendations for the practical application of considered metamaterial structure for designing patch antennas have been discussed.     

New trends in solar photovoltaics: From physics to chemistry

The paper briefly discusses the current situation in the field of traditional and unconventional photovoltaic materials and solar cells. It emphasizes the fact that the main basic achievements in the field of solid-state solar photovoltaics were gained at least two decades ago and the further progress focused on the improvement of cell parameters and technological aspects. Finally, the article concludes that this scientific area has nearly fulfilled its historical task. Indeed, the last decade has brought many new achievements in the field of the alternative, molecular-based materials. The future of solar energy conversion seems to be mainly connected with chemistry, chemical physics and chemical engineering but not with solid-state physics as in the twentieth century. The paper gives also a short over-view of some promising organic semiconductors, fullerenes and TiO₂ nanocrystalline structures used now in a new generation of molecular solar cells. Presented at the Int’l Symp. on Chem. Eng. (Cheju, Feb. 8–10, 2001), dedicated to Prof. H. S. Chun on the occasion of his retirement from Korea University     

The atmospheric integral transparency coefficient and the Forbes effect

The Forbes effect (known from 1842) expresses the fact that a total (broadband) direct solar beam becomes increasingly penetrating on its way through the atmosphere – because of changes in its spectral content and loss of less penetrating spectral components. The effect restricts the use of the Bouguer-Lambert law for calculating the characteristics of transparency (or turbidity) of the air. Efforts to overcome this effect and to transform the coefficients of transparency to a given solar elevation have finally met with success, and in this study one of such methods (developed by Mürk and Ohvril) is presented in detail. This method is compared with those of Evnevich and Savikovskij. For solar elevations 20°≤h≤80° all three techniques are compatible, securing accuracy with an uncertainty below 2.5% with regard to standard values of the coefficient of transparency. Simple transition to the Linke turbidity factor is available. Time courses of mean annual values of the coefficient of atmospheric transparency at solar elevation h=30° and the Linke factor for the last 40 years at an Estonian station at Tiirikoja are given as examples. In the average the multiannual time courses demonstrate an increase of atmospheric turbidity as well as bear evidence of sensitivity to great volcanic eruptions.     

Accurate Analysis of Tumor Margins Using a Fluorescent pH Low Insertion Peptide (pHLIP)

The recurrence of certain cancers remains quite high due to either incomplete surgical removal of the primary tumor or the presence of small metastases that are invisible to the surgeon. Near infrared (NIR) fluorescence imaging might improve surgical outcomes by providing sensitive, specific, and real-time visualization of normal and diseased tissues if agents can be found that discriminate between normal and diseased tissue and define tumor margins. We have developed a new approach for revealing tumor borders by using NIR fluorescently labeled pH Low Insertion Peptide (pHLIP) and have created a computational program for the quantitative assessment of tumor boundaries. The approach is tested in vivo by co-localization of GFP-tumors and NIR emission from the fluorescently labeled pHLIP, and it is found that boundaries are accurately reported and that sub-millimeter masses can be detected.     

Characterization of phases formed in the iron carbide process by X-ray diffraction, mossbauer, X-ray photoelectron spectroscopy, and raman spectroscopy analyses

Iron carbide was prepared by iron ore reduction and iron cementation using Ar-H₂-CH₄ gas mixture with and without sulfur. Phases formed in the reduction/cementation process were examined by X-ray diffraction (XRD), Mossbauer, and Raman spectroscopy. The sample surface was also analyzed by X-ray photoelectron spectroscopy (XPS). XRD and Mossbauer analyses showed that iron oxide was first reduced to metallic iron, and then, metallic iron was carburized to cementite. Addition of a small amount of H₂S to the reaction gas retarded the cementite formation but made the cementite more stable. XPS analysis showed that the surface of samples converted to iron carbide using sulfurcontaining gas consisted of mainly Fe₃C and a small amount of graphitic carbon. Raman spectra of a sample produced in the iron carbide process showed the G and D bands, which are characteristic for carbon-carbon bonds. The intensity ratio of G/D bands depended on the sulfur content in the reducing/carburizing gas.     

A formal procedure and invariants of a transition from conventional finite elements to the absolute nodal coordinate formulation

In this paper, finite elements based on the absolute nodal coordinate formulation (ANCF) are studied. The formulation has been developed by various authors for the dynamical simulation of large-displacement and large-rotation problems in flexible multibody dynamics. This study introduces a procedure to track the general geometrical properties of ANCF elements back to their prototypes in the conventional finite-element method (FEM), which deals with small-displacement problems. In this study, it is shown that each known ANCF element can be derived from a conventional FEM using a universal transform. Moreover, some important static and dynamic properties of the elements in small-displacement problems are automatically preserved. In the past, the authors of each newly proposed ANCF element have made unnecessary efforts to show the consistency of the above mentioned properties.